This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Amyloid fibrils are self-assembled filaments with typical length of 0.1-10 um and approximate width of 10nm in electron microscopy images, formed by the spontaneous aggregation of a wide variety of peptides and proteins. Current interest in amyloid fibrils within the biomedical research community stems from the factor that the amyloid fibrils in the affected organs causes the amyloid diseases. Amyloid diseases, including Alzheimer's disease, type 2 diabetes, prion diseases as well as Parkinson's disease, constitute major public health problems. Biochemical analysis of the amyloid peptides isolated from Alzheimer's disease brain indicates that amyloid beta (A-beta) (1-42) are the principle species associated with senile plaque amyloid, while A-beta (1-40) is more abundant in cerebrovascular amyloid deposit. Interest within the biochemical and biophysical research communities arises primarily from fundamental questions regarding the nature of the interactions that make amyloid fibrils such a stable structure for a polypeptide chain, and the mechanisms by which amyloid fibrils form from monomeric or oligomeric species. In our proposed study, polymerization of both A-beta (1-42) and A-beta (1-40) will be investigated using single molecule techniques. Fluorescence correlation spectroscopy (FCS), a technique with single molecule detection sensitivity and capable of detecting small molecules (monomer, dimmer) and large aggregates (amyliod fibrils) simutaneously in solution is developed for studying the process of polymerization of both A-beta (1-42) and A-beta (1-40). Fluorescence resonance energy transfer (FRET) will also be used to study the initial steps from the monomer to dimer and trimer aggregation of this polymerization process of amyloid fibrils at the single molecule level.